Nearly half of all college students have a diagnosable mental health problem (Blanco et al., 2008). College counseling centers (CCCs) are faced with increasing demands for services from Universities, students, and parents to meet the treatment needs of their students (Kay and Schwartz, 2010), in the context of increasingly severe cases and declining resources (Gallagher, 2013). Innovative, cost effective solutions are needed that can improve treatment effectiveness with a range of presenting problems while reducing counselor workloads. The proposed Phase II SBIR project seeks to meet these needs by completing the development and evaluation of a web-based guided self-help version of Acceptance and Commitment Therapy (ACT; Hayes, Strosahl and Wilson, 1999), an acceptance and mindfulness-based transdiagnostic therapy found to effectively treat a range of mental health problems, by targeting experiential avoidance (EA), the tendency to avoid unwanted emotions and negative thoughts (Hayes et al., 2006). A guided self-help ACT website would provide a means of implementing effective treatment for the range of problems encountered in the CCC setting, while the online guided self-help format would reduce counselors' workload for each client, improving cost-effectiveness, and reducing waiting lists. This product would both treat students through a series of self- help modules, while training CCC counselors in the basics of ACT and how to implement the guided self-help intervention, and providing them tools to monitor and follow up with student clients using the program. In Phase I, a prototype of ACT on College Life (ACT-CL) was developed and evaluated in an open trial with 30 counselors and 82 student clients across 4 CCCs. Results provided support for the usability, feasibility and potential effectiveness of the product. In Phase II, the full ACT-CL product will be developed. The final student portal will include eight 30-minute self-help sessions targeting the core processes in ACT, tailored to a problem of the user's choosing, as well as mobile app and ACT Toolbox features (i.e., saving favorite skills to review later). The counselor portal will include a series of training modules on guided self-help and ACT, interactive forum, system to add student users and monitor their program usage, and a secure messaging system to contact students. Program content will be revised through focus groups with students in CCC treatment (n = 16), focused interviews with counselors (n = 8) and usability testing (10 counselors and 10 students in treatment). The final program will be evaluated in a randomized controlled trial comparing CCC treatment as usual (TAU) to TAU plus the ACT-CL program (ACT+TAU) with 40 counselors and 400 student clients (10 clients/counselor) on measures of mental health, program satisfaction, and mechanisms of change. ACT-CL will be subsequently marketed to CCCs across the US and abroad via the sale of site licenses.